Traditional soil compacters, e.g., reversible vibration plates and vibration rollers, are equipped with a contrarotating unbalance shaft pair for generating directed oscillations. The unbalances of the two shafts rotate synchronously but with the opposite directions of rotation. A desired, directed direction of oscillation can be adjusted by phase shifting, and a directed forward or reverse movement of the soil compacter can be produced.
However, a periodically changing tipping moment is produced as a function of the phase position of the unbalances. This tipping moment occurs because the individual unbalances have different axes of rotation. As a consequence, the resulting centrifugal force of two unbalance shafts always is applied at another point during the course of a rotation. The direction of the resulting force does remain the same, but the effective lever arm and the magnitude of the force change. This tipping moment is undesirable because it has a disadvantageous effect on the behavior of the movement of the soil compacter.
DE 297 23 617 U1 teaches a vibration plate comprising a tipping moment compensating device for suppressing such a tipping moment. It comprises a central unbalance shaft between a pair of unbalance shafts. The unbalance mass of the central unbalance shaft is as great as the entire unbalance mass of the pair of unbalanced shafts. The central unbalance shaft rotates counter to the unbalance shaft pair rotating in the same direction, and the speed of all unbalance shafts is synchronous. As a result of this arrangement no undesired tipping moment occurs.